With the development of economy, massive and dispersed 5G base stations (BSs) and distributed photovoltaics (DPVs) will be widely integrated into the grid. Considering the backup energy storage equipped with 5G BSs is a flexible resource with considerable capacity and great potential, a model to evaluate and quantify BS dispatchable capacity, and a cluster partition method to bundle BSs with DPVs are established. Based on these, a bi-layer optimization model of energy storage system (ESS) planning is proposed, which can simultaneously obtain the optimal ESS capacity, power and location determination scheme and scheduling schemes of ESSs and 5G BSs. The simulation results demonstrate that the proposed planning method reduces the ESS investment, increasing the system economy and low carbon benefits.